@EternalSnowman &
@Walter_vi_Britannia: Actually, it's normal in Japanese to use 兄弟 (kyoudai, lit. "older brother(s) and younger brother(s)") as a catch-all term for siblings regardless of sex; this is reflected in the existence of 男兄弟 and 女兄弟 as specific terms for "male siblings" and "female siblings", as well as the words 姉妹 (shimai, lit. "older sister(s) and younger sister(s)"), 兄姉 (keishi, lit. "older brother and older sister(s)"), 兄妹 (keitei, lit. "older brother and younger sister(s)"), and 姉弟 (shitei, lit. "older sister(s) and younger brother(s)") all have
kyoudai as a valid (though irregular) alternate pronunciation. And if you look up the Japanese translations of terms with "sibling" (e.g. "half-sibling"), you'll find that they commonly use 兄弟.
The language also has 兄弟姉妹 (kyoudaishimai, lit. "older brother(s), younger brother(s), older sister(s) and younger sister(s)"), but the lengthiness of the word probably explains why 兄弟 got its gender-neutral connotation.